Network node and method for managing power of cell reference symbols

ABSTRACT

A method performed by a network node for managing power of Cell Reference Symbols, CRS, wherein the network node operates one or more cells and the network node is configured to transmit the CRS in a first power mode. When the network node identifies a first cell which is not actively serving any UEs, which cell is also referred to as an empty cell, the network node reduces the power of the CRS in the first cell in relation to the first power mode. By reducing the power of the CRS, the overall interference of the CRS from the empty cell is reduced, thereby enhancing the performance in cells actively serving UEs.

This application is a 371 of International Application No.PCT/SE2014/050993, filed Aug. 28, 2014, the disclosure of which is fullyincorporated herein by reference.

TECHNICAL FIELD

Embodiments herein relate to a network node and a method therein. Inparticular, it relates to a method for managing power of Cell ReferenceSymbols.

BACKGROUND

Communication devices such as User Equipments (UEs) are enabled tocommunicate wirelessly in a cellular communications network or wirelesscommunication system, sometimes also referred to as a cellular radiosystem or cellular networks. The communication may be performed e.g.between two UEs, between a UE and a regular telephone and/or between aUE and a server via a Radio Access Network (RAN) and possibly one ormore core networks, comprised within the cellular communicationsnetwork.

UEs may further be referred to as wireless terminals, mobile terminalsand/or mobile stations, mobile telephones, cellular telephones, laptops,tablet computers or surf plates with wireless capability, just tomention some further examples. The UEs in the present context may be,for example, portable, pocket-storable, hand-held, computer-comprised,or vehicle-mounted mobile devices, enabled to communicate voice and/ordata, via the RAN, with another entity, such as another wirelessterminal or a server.

The cellular communications network covers a geographical area which isdivided into cell areas, wherein each cell area being served by anetwork node. A cell is the geographical area where radio coverage isprovided by the network node.

The network node may further control several transmission points, e.g.having Radio Units (RRUs). A cell can thus comprise one or more networknodes each controlling one or more transmission/reception points. Atransmission point, also referred to as a transmission/reception point,is an entity that transmits and/or receives radio signals. The entityhas a position in space, e.g. an antenna. A network node is an entitythat controls one or more transmission points. The network node may e.g.be a base station such as a Radio Base Station (RBS), eNB, eNodeB,NodeB, B node, or BTS (Base Transceiver Station), depending on thetechnology and terminology used. The base stations may be of differentclasses such as e.g. macro eNodeB, home eNodeB or pico base station,based on transmission power and thereby also cell size.

Further, each network node may support one or several communicationtechnologies. The network nodes communicate over the air interfaceoperating on radio frequencies with the UEs within range of the networknode. In the context of this disclosure, the expression Downlink (DL) isused for the transmission path from the base station to the mobilestation. The expression Uplink (UL) is used for the transmission path inthe opposite direction i.e. from the UE to the base station.

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE),base stations, which may be referred to as eNodeBs or even eNBs, may bedirectly connected to one or more core networks. In LTE the cellularcommunication network is also referred to as E-UTRAN.

An E-UTRAN cell is defined by certain signals which are broadcasted fromthe eNB. These signals contain information about the cell which can beused by UEs in order to connect to the network through the cell. Thesignals comprise reference and synchronization signals which the UE usesto find frame timing and physical cell identification as well as systeminformation which comprises parameters relevant for the whole cell.

A UE needing to connect to the network must thus first detect for asuitable cell, as defined in 3GPP TS 36.304 v11.5.0. This is performedby measuring on received reference signals sent by neighboring cells,also referred to as “listening” for a suitable cell. The suitable cellis commonly the cell with best quality of signal. Listening for asuitable cell may comprise searching for synchronization signalstransmitted from the network node in an OFDM subframe. When a suitablecell is found the UE performs random access, according to a systeminformation for the cell. This is done in order to transmit a RadioResource Control (RRC) connection setup request to the network node.Assuming the random access procedure succeeds and the network nodereceives the request, the network node will either answer with an RRCconnection setup message, which acknowledges the UEs request and tellsit to move into RRC connected state, or an RRC connection reject, whichtells the UE that it may not connect to the cell. In RRC connected statethe parameters necessary for communication between the network node andthe UE are known to both entities and a data transfer between the twoentities is enabled.

To facilitate handover to other cells, each network node may store cellidentities that are supported by the other network nodes in an addressdatabase, in order to know how to contact the network node of potentialtarget cells for handover. Each network node serving a cell typicallystores in the data base which cells it has neighbor relations to, i.e.which of the cells in the area UEs often perform handover to. The cell'sneighbor relations will hereafter be referred to as the cell's “neighborrelation list”.

Cell specific Reference Signals (CRS) are UE known symbols that areinserted in a Resource Element (RE) of a subframe of an OrthogonalFrequency-Division Multiplexing (OFDM) time and frequency grid andbroadcasted by the network node. Each RE has an extension in thefrequency domain corresponding to an OFDM sub carrier and an extensionin the time-domain corresponding to an OFDM symbol interval.

The CRS are used by the UE for downlink channel estimation. Channelestimation is used for demodulation of downlink data both when the UE isin RRC connected state and is receiving user data and when the UE is inRRC idle state and is reading system information. Due to the latter usecase, the CRSs must be transmitted even from cells which do not have anyUEs in RRC connected state since the eNB cannot know whether a UE wantsto access the network until it performs random access. Downlink cellspecific reference signals are inserted within the first and third lastOFDM symbol of each slot with a frequency domain spacing of sixsub-carriers. A slot is a time period of the OFDM time and frequencygrid, which is usually 0.5 msec long. A problem with the knowntechnology is therefore that cells without any UEs in RRC connectedstate still consume power due to CRS broadcasting.

In case several antennas are used by the network node for transmittingand each antenna is representing a cell, each antenna has to transmit aunique reference signal in order for the UE to connect to that specificcell. When one antenna transmits, the other antennas have to be silentin order not to interfere with the first antennas reference signal. Toreduce the interference of reference signals between the cells, theposition of the CRS is usually shifted in frequency between the cells.The CRS can be shifted between 0-5 sub carriers, each sub carriercorresponding to a frequency shift of 15 kHz for LTE. The cell specificfrequency shift can be derived from the physical Cell Identity (Cell ID)which is signaled to the UE by selection of appropriate PrimarySynchronization Channel (PSCH) and Secondary Synchronization Channel(SSCH

Although this solution reduces the interference of reference symbolsbetween cells, it has the problem that the reference symbols of one cellwill disturb Physical Downlink Shared Channel (PDSCH) and PhysicalDownlink Control Channel (PDCCH) symbols of neighboring cells.

Hence, even though cells do not have any UEs in RRC connected state,disturbance may impact UE DL throughput in neighboring cells. This willespecially be the case when the UE is in and/or close to borders betweencells.

Reducing the power of the CRS may mitigate this problem. However, inorder to access a cell the UE must be able to hear the CRS of the cell,i.e. the UE must be able to recognize and receive the CRS transmittedfrom the cell. Therefore reducing the power of the CRS also shrinks thesize of the cell, since more distant UEs no longer will hear the CRS.Furthermore, the quality of the channel estimates used for demodulationdecreases when the Signal to Interference Ratio (SINR) on the CRSdecreases. Reducing the power of the CRS therefore causes degradation ofcell edge performance. This degradation is further aggravated when theload in the network increases, especially if the data is transmittedwith higher power than the CRS, which is usually the case when theeffect of CRS interference is to be reduced.

SUMMARY

It is therefore an object of embodiments herein to enhance theperformance in a wireless communications network.

According to a first aspect of embodiments herein, the object isachieved by a method performed by a network node for managing power ofCell Reference Symbols, CRS. The network node operates one or more cellsand is configured to transmit the CRS in a first power mode. When afirst cell is identified, which first cell is not actively serving anyUEs, the network node reduces power of the CRS in the first cell inrelation to the first power mode.

According to a second aspect of embodiments herein, the object isachieved by a network node for performing the method for managing powerof Cell Reference Symbols, CRS. The network node operates one or morecells and is configured to transmit the CRS in a first power mode. Thenetwork node is configured to identify a first cell that is not activelyserving any UEs in RRC connected mode. The network node further isconfigured to reduce power of the CRS in the first cell in relation tothe first power mode.

By reducing the power of the CRS in cells that do not serve any UEs inRRC connected mode, the power consumption and the interference fromempty cells can be reduced, thereby enhancing the performance of cellsthat have UEs in RRC connected mode. In a non-loaded system, reducingthe power of the reference symbols will reduce interference and increasesingle UE throughput when CRSs are shifted in the frequency domain.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments herein are described in more detail withreference to attached drawings in which:

FIG. 1 is a schematic block diagram illustrating embodiments of awireless communications network.

FIG. 2 is a schematic block diagram illustrating embodiments of an OFDMsubframe.

FIG. 3 is a flowchart depicting embodiments of a method in a networknode.

FIG. 4 is a schematic block diagram illustrating embodiments of anetwork node.

DETAILED DESCRIPTION

FIG. 1 depicts an example of a wireless communications network 100according to a first scenario in which embodiments herein may beimplemented. The wireless communications network 100 is a wirelesscommunication network such as an LTE, E-Utran, WCDMA, GSM network, any3GPP cellular network, Wmax, or any cellular network or system.

The wireless communications network 100 comprises a plurality of networknodes whereof two, a first network node 110 and a second network node111 are depicted in FIG. 1. The first network node 110 and the secondnetwork node 111 are network nodes which each may be a transmissionpoint such as a radio base station, for example an eNB, an eNodeB, or anHome Node B, an Home eNode B or any other network node capable to servea wireless terminal such as UE or a machine type communication device ina wireless communications network. The first network node 110 and thesecond network node 111 each serves a plurality of cells 130, 131, 132.

The wireless communications network 100 comprises a UE 120. The firstnetwork node 110 and the second network node 111 may each be atransmission point for the wireless terminal 120. The UE 120 is withinradio range of the first network node 110 and the second network node111, this means that it can hear signals from the first network node 110and the second network node 111.

The UE 120 may e.g. be a wireless terminal, a wireless device, a mobilewireless terminal or a wireless terminal, a mobile phone, a computersuch as e.g. a laptop, a Personal Digital Assistant (PDA) or a tabletcomputer, sometimes referred to as a surf plate, with wirelesscapability, or any other radio network units capable to communicate overa radio link in a wireless communications network. Please note the termwireless terminal used in this document also covers other wirelessdevices such as Machine to machine (M2M) devices.

FIG. 2 shows an exemplary downlink OFDM time and frequency grid, whichis also referred to as an OFDM subframe. Each subframe comprises twoslots. Each slot comprising a number of resource elements (RE) 201extending both in the time domain (x-axis) and in the frequency domain(z-axis). Each RE's 201 extension in the frequency domain is referred toas a sub-carrier whereas the extension in the time domain is referred toas an OFDM symbol. As can be seen in FIG. 2, the first OFDM symbolcomprises control signaling and CRS which carries the necessaryinformation about the network node 110 to allow the UE 120 to connect toit. The control signaling is located in the beginning of each subframe,also known as the control region of the subframe, and spans the fullbandwidth of the subframe. FIG. 2 shows an exemplary size of a normalcontrol region of three OFDM symbols, the size of the control region mayhowever be dynamically adjusted according to the current trafficsituation.

The CRS are used by the UE 120 for downlink channel estimation. Channelestimation is used for determining the demodulation of downlink databoth when the UE 120 is in RRC connected state and is receiving userdata and when the UE 120 is in RRC idle state and is reading systeminformation. Downlink CRS are inserted within the first and third lastOFDM symbol of each slot with a frequency domain spacing of sixsub-carriers.

The subframe also comprises data symbols used for transmitting user databetween the network node 110 and the UE 120. The data symbols aresituated in the region following the control region, which is alsoreferred to as the data region.

Example of embodiments of a method in the network node 110 for managingpower of CRS, will now be described with reference to a flowchartdepicted in FIG. 3. The network node 110 operates one or more cells andis configured to transmit the CRS in a first power mode duringoperation. This relates to normal operation. The first power mode mayalso be referred to as the normal power mode which is used when the atleast one cell of the network node 110 is serving at least one UE 120 inRRC connected mode. In this power mode CRS and data symbols aretransmitted with the same power, i.e. the power difference between theCRS and the data symbols is zero or almost zero.

The method comprises the following actions, which actions may be takenin any suitable order. Dashed lines of a box in FIG. 3 indicate thatthis action is not mandatory.

Action 301

The network node 110 identifies a first cell 130 which is not activelyserving any UEs 120 in RRC connected mode. When the cell is not activelyserving any UEs 120, the cell is referred to as an empty cell.

The cell is not actively serving any UEs 120 when the network node 110has not sent or received any messages to/from any UEs 120 in the cellwithin a predetermined time, and/or when the cell does not have any UEs120 in RRC connected mode.

The cell may switch from not actively serving any UEs 120 to activelyserving UEs in case of certain events. Events that trigger a switch maye.g. be that the network node 110 sends a page message in the cell 130,receives a random access preamble in the cell 130 or sends a randomaccess response in the cell 130. It may further be triggered when thenetwork node sends/receives Common Control Channel messages, DedicatedControl Channel messages and/or Dedicated Traffic Channel messages inthe cell 130.

Action 302

When the network node 110 has identified a first cell 130 which is notactively serving any UEs 120, i.e. an empty cell 130, the network node110 reduces the power of the CRS in the first cell 130 in relation tothe first power mode. This reduced power mode may also be referred to aslow power mode. By reducing the power of the CRS to a power level lowerthan the power level of the data symbols, the overall interference ofthe CRS from the empty cell 130 is reduced.

In some embodiments the reduced CRS power is applied on CRS which aresent on any Orthogonal Frequency-Division Multiplexing (OFDM) symbol ofa subframe, except the first OFDM symbol of the subframe. By applyingthe reduced CRS power on all the OFDM symbols except the first OFDMsymbol, the interference by the CRS is reduced while at the same timeallowing UEs 120 to hear the CRS from the empty cell 130.

The network node 110 holds the reduced CRS power as long as the cell 130is determined not to actively serve any UEs 120.

The CRS power may further be adapted in several levels. Possible valuesfor the reduced power levels may be e.g. −3, −2, −1 dB compared to theother symbols, thereby allowing a reduction of power in three steps.However, other and/or further power levels may also be used.

The power difference may be signaled to the UE 120 in the systeminformation where it may be used to improve the demodulation performancefor modulation types which carry information in the amplitude domain.The modulation scheme used may be e.g. be 16 QAM, 64 QAM and/or anyother modulation schemes which carries information in the amplitudedomain.

In a further embodiment a hysteresis function may be applied whenchanging CRS power level, thereby avoiding unnecessary switching betweenthe power modes when the cell 130 is switching from not actively servingany UEs 120 to actively serving UEs very quickly.

Action 303

The network node 110 may further send information about CRS power andthe number of RRC connected UEs 120 of each cell, to neighboring cellslisted in a neighbor relation list. The neighboring cells may beconnected to the same or to different network nodes 111. The informationmay be sent via an X2 interface when a neighboring cell is served by another network node 111. In a further embodiment the information may besent over a S1 interface via a Mobility Management Entity (MME).

When the UE 120 wants to connect to a network node 110, it measures theaverage Received CRS Power (RSRP) from each cell it can hear, and usesthat information to decide which of the cells is suitable to connect to.The RSRP may also be used for connected state mobility, where thenetwork node 110 uses layer 3 measurement reports from the UE 120 senton the uplink shared channel to support handover decisions. Such areport may for example state that the UE 120 is about to move out ofcoverage of its current serving cell. However, 3GPP offers a set oftools and mechanisms which the network node 110 can configure in the UE120 in order to get other reports which are relevant and needed. Oneexample is the A3 event in which the network node 110 configures the UE120 to send the RSRP of both the serving cell and neighbor cells shouldthe neighbor RSRP become sufficiently strong compared to the servingcell. This information may then be forwarded to the neighboring cells bythe network node 110.

Action 304

In some embodiments the network node 110 also receives information aboutthe CRS power mode and number of actively served UEs 120 in neighboringcells. The information may be received from neighboring network nodes111. When the information is received from a neighboring network node111 it may be received via the X2 interface.

In a further embodiment the information may also be received over the S1interface via the MME.

The information may be used to allow the network node 110 to configureCell Individual Offsets (CIO) with both positive and negative values.The UE 120 may add the CIO for a given cell to the measured RSRP of thatcell, in order to compensate for the low CRS power level of that cell.By doing so the UE 120 may connect to another cell, e.g. the empty cell130, even though the RSRP is lower for the empty cell 130 than foranother cell 131, 132 with actively served UEs 120. CIO can beconfigured both in IDLE mode, where it is broadcasted in SystemInformation Blocks (SIB), and in connected mode, where it is sent in adedicated RRC configuration to each UE 120.

Action 305

When the network node has received the information about neighboringcells it may use this information to identify a second cell 131, whichcell 131 is actively serving at least one UE 120 and is neighbouring acell 132 where the number of actively served UEs 120 exceeds a firstthreshold, based on the information received in action 304.

Action 306

When the network node has identified a second cell 131 according toaction 305, it may increase the power of the CRS in the second cell 131in relation to the first power mode. By increasing the power of the CRSin the second cell 131, UEs located in the surrounding cells are able tomore easily detect the second cell in order to connect to it.

The CRS power may also be increased in several levels. Possible valuesfor the increased power levels may be e.g. 1.77 and 3 dB compared to theother symbols, thereby allowing an increase of power in two steps.However, other and/or further power levels may also be used.

By increasing the power of the CRS in the second cell 131, UEs locatedin the surrounding cells are able to more easily detect the second cellin order to connect to it.

To perform the method actions for managing power of Cell ReferenceSymbols, (CRS) described above in relation to FIG. 2, the network node110 comprises the following arrangement depicted in FIG. 4. As mentionedabove the network node 110 operates one or more cells and is normallyconfigured to transmit the CRS in a first power mode.

The network node 110 comprises a radio circuitry 401 to communicate withUEs 120, a communication circuitry 402 to communicate with other networknodes and a processing unit 403.

The network node 110 is configured to, e.g. by means of an identifyingmodule 404 being configured to, identify a first cell 130 that is notactively serving any UEs 120. The network node 110 is further configuredto, or comprises a power regulating module 405 configured to, reducepower of the CRS in the first cell 130 in relation to the first powermode, when a first cell is identified not to actively serve any UEs 120.

In some embodiments herein, the network node 110 may further beconfigured to, e.g. by means of a sending circuitry 406 being configuredto, send information about the CRS power mode and the number of activelyserved UEs 120 to neighbouring network nodes 111. In one embodiment themeans to send information about the CRS power mode and the number ofconnected UEs 120 to neighbouring network nodes 120 may be an X2interface. The sending circuit 406 may be comprised in the communicationcircuitry 402.

In a further embodiment the network node 110 may be configured to, e.g.by means of a receiving circuitry 407 being configured to, receiveinformation about the CRS power mode and number of actively served UEs120 in neighbouring cells. The information is received from theneighboring network nodes 111. The receiving circuit 407 may becomprised in the communication circuitry 402.

The network node 110 may further be configured to, or may comprise theidentifying module 404 further being configured to, identify a secondcell 131, which cell 131 is actively serving at least one UE 120 and isneighbouring a cell 132 where the number actively served UEs 120 exceedsa first threshold.

In a further embodiment the network node is configured to, or comprisesthe power regulating unit 405 further being configured to, increase theCRS power in the second cell 131 in relation to the first power modewhen the number of actively served UEs 120 in the neighboring cell 132exceeds the first threshold.

In order to reduce unnecessary switching between the power modes, thenetwork node 110 may further be configured to, or may comprise the powerregulating unit 405 further being configured to reduce and/or increasethe CRS power using a hysteresis function. By using a hysteresisfunction the network node 110 may not switch power mode immediately whenthe number of actively served UEs 120 changes, but will remain in onepower mode for a certain amount of time after the change of activelyserved UEs 120 has taken place.

The embodiments herein for managing power of Cell Reference Symbols,(CRS) may be implemented through one or more processors, such as theprocessing unit 403 in the network node 110 depicted in FIG. 3, togetherwith computer program code for performing the functions and actions ofthe embodiments herein. The program code mentioned above may also beprovided as a computer program product, for instance in the form of adata carrier carrying computer program code for performing theembodiments herein when being loaded into the in the network node 110.One such carrier may be in the form of a CD ROM disc. It is howeverfeasible with other data carriers such as a memory stick. The computerprogram code may furthermore be provided as pure program code on aserver and downloaded to the network node 110.

Those skilled in the art will also appreciate that the identifyingmodule 404 and power regulating module 405 described above may refer toa combination of analog and digital circuits, and/or one or moreprocessors configured with software and/or firmware, e.g. stored in thememory 408, that when executed by the one or more processors such as theprocessing unit 403 as described above. One or more of these processors,as well as the other digital hardware, may be included in a singleApplication-Specific Integrated Circuitry (ASIC), or several processorsand various digital hardware may be distributed among several separatecomponents, whether individually packaged or assembled into asystem-on-a-chip (SoC).

The network node 110 may further comprise a memory 408 comprising one ormore memory units. The memory 409 is arranged to be used to storeobtained information, measurements, data, configurations, schedulings,and applications to perform the methods herein when being executed inthe network node 110.

When using the word “comprise” or “comprising” it shall be interpretedas non-limiting, i.e. meaning “consist at least of”.

The embodiments herein are not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appending claims.

The invention claimed is:
 1. A method performed by a network node formanaging power, wherein the network node operates one or more cells, themethod comprising: transmitting Cell Reference Symbols (CRS) in a firstpower mode, wherein in the first power mode the CRS and data symbols aretransmitted with a same power; when a first cell is identified that isnot actively serving any User Equipments (UEs), reducing power of theCRS in the first cell in relation to the first power mode, wherein thereduced power is applied on the CRS that are sent on all OrthogonalFrequency-Division Multiplexing (OFDM) symbols of a subframe, except afirst OFDM symbol of the subframe; and when the first cell is determinedto actively serve at least one UE: receiving, from neighbouring networknodes, information about a CRS power mode and a number of activelyserved UEs in neighbouring cells; identifying, based on the receivedinformation from the neighbouring network nodes, a second cell that isactively serving at least one UE and is neighbouring a cell where thenumber of actively served UEs exceeds a threshold; and increasing theCRS power in the second cell in relation to the first power mode.
 2. Themethod according to claim 1, wherein the method further comprises:sending information about the CRS power and a number of Radio ResourceControl (RRC) connected UEs to one or more neighbouring network nodes.3. The method according to claim 2, wherein the information is sent viaan X2 interface.
 4. The method according to claim 1, wherein reducingand/or increasing the CRS power is performed using a hysteresisfunction.
 5. The method of claim 1, wherein the identifying the firstcell as not actively serving any UEs comprises one or more of:determining that the first cell has not sent or received any messages toany UEs within a predetermined time; or determining that the first cellis not operating with any UEs in a connected mode.
 6. The method ofclaim 1, wherein the determining when the first cell actively serves atleast one UE is based on one or more of the following: the network nodereceiving a random access preamble in the first cell or sending a randomaccess response in the first cell; or the network node sending orreceiving a page message, a Common Control Channel message, a DedicatedControl Channel message, or a Dedicated Traffic Channel message in thefirst cell.
 7. The method of claim 1, further comprising: maintainingthe reduced power of the CRS in the first cell while the first cell isdetermined to not actively serve any UEs.
 8. The method of claim 1,further comprising: signaling a power difference to at least one UE, thepower difference based on the reduced power of the CRS in the first cellin relation to the first power mode.
 9. The method of claim 1, whereinthe reducing of the power of the CRS in the first cell further includesthe network node configuring Cell Individual Offsets (CIO) for the firstcell.
 10. A network node for managing power, wherein the network nodeoperates one or more cells, the network node further being configuredto: transmit Cell Reference Symbols (CRS) in a first power mode, whereinin the first power mode the CRS and data symbols are transmitted with asame power; identify a first cell that is not actively serving any UserEquipments (UEs); reduce power of the CRS in the first cell in relationto the first power mode, wherein the reduced power is applied on the CRSthat are sent on all Orthogonal Frequency-Division Multiplexing (OFDM)symbols of a subframe, except a first OFDM symbol of the subframe;receive, from neighbouring network nodes, information about a CRS powermode and a number of actively served UEs in neighbouring cells;identify, based on the received information from the neighbouringnetwork nodes, a second cell that is actively serving at least one UEand is neighbouring a cell where the number of actively served UEsexceeds a threshold; and increase the CRS power in the second cell inrelation to the first power mode.
 11. The network node according toclaim 10, wherein the network node further is configured to: sendinformation about the CRS power mode and the number of actively servedUEs to one or more neighbouring network nodes.
 12. The network nodeaccording to claim 10, wherein sending information about the CRS powermode and the number of actively served UEs to the neighbouring networknodes is performed using an X2 interface.
 13. The network node accordingto claim 10, wherein the network node further is configured to: reduceand/or increase the CRS power using a hysteresis function.
 14. Thenetwork node according to claim 10, wherein the identifying the firstcell as not actively serving any UEs comprises one or more of:determining that the first cell has not sent or received any messages toany UEs within a predetermined time; or determining that the first cellis not operating with any UEs in a connected mode.
 15. The network nodeaccording to claim 10, wherein the determining when the first cellactively serves at least one UE is based on one or more of thefollowing: the network node receiving a random access preamble in thefirst cell or sending a random access response in the first cell; or thenetwork node sending or receiving a page message, a Common ControlChannel message, a Dedicated Control Channel message, or a DedicatedTraffic Channel message in the first cell.
 16. The network nodeaccording to claim 10, further comprising: maintaining the reduced powerof the CRS in the first cell while the first cell is determined to notactively serve any UEs.
 17. The network node according to claim 10,further comprising: signaling a power difference to at least one UE, thepower difference based on the reduced power of the CRS in the first cellin relation to the first power mode.
 18. The network node according toclaim 10, wherein the reducing of the power of the CRS in the first cellfurther includes the network node configuring Cell Individual Offsets(CIO) for the first cell.